Process for the manufacture of butanol or acetone

ABSTRACT

A process for the manufacture of butanol, acetone and/or other renewable chemicals is provided wherein the process utilises one or more of the group comprising by-products of the manufacture of malt whisky, such as draff, pot ale and/or spent lees, biomass substrates, such as paper, sludge from paper manufacture and spent grains from distillers and brewers, and diluents, such as water and spent liquid from other fermentations. The process comprises treating a substrate to hydrolyse it and fermenting the treated substrate at an initial pH in the range of 5.0 to 6.0. Also provided is a biofuel comprising butanol manufactured according to the process of the invention.

FIELD OF THE INVENTION

The present invention relates to a process for the manufacture ofbiofuels and renewable chemicals. More particularly, the inventionrelates to a process for the manufacture of butanol. The inventionfurther relates to a process for the manufacture of acetone.

BACKGROUND TO THE INVENTION

In recent years, higher oil prices, depleting fuel supplies andenvironmental concerns have led to a renewed interest in the productionof fuels from biomass (“biofuels”). Biobutanol is produced byfermentation of biomass using bacteria, typically of the genusClostridium. In addition to butanol, these organisms also produceacetone, which is an important solvent, and ethanol so the process isoften referred to as “ABE process” (Acetone/Butanol/Ethanol process).Currently used feedstocks or substrates include energy crops, such assugar beets, sugar cane, corn grain and wheat, as well as agriculturalby-products, such as straw and corn stalks. The use of biobutanol as afuel has several advantages over the use of ethanol. However, asbiobutanol production is currently more expensive than ethanolproduction it has not been commercialized on a large scale.

Malt whisky refers to whisky which has been produced from no grain otherthan malted barley. Production of malt whisky begins with malting ofbarley by steeping the barley in water. Malting releases enzymes thatbreak down starches in the grain and convert them into sugars. When thedesired state of germination is reached, the malted barley is dried. Thedried malted barley is mashed in a mash-tun. In mashing, the enzymesthat were developed during the malting process are allowed to convert orhydrolyse the barley starch into sugar. The resulting liquid whichcontains the sugars is referred to as wort. This is transferred to alarge vessel called a washback where it is cooled and allowed to fermentto form the “wash”. The residue remaining after extraction of thesoluble sugars or wort is known as draff. This comprises spent barleysolids or spent grains.

The wash is distilled in a copper distillation vessel or pot still knownas a wash still to produce an alcohol-containing liquid distillate,known as low wines. The distillation residue or liquor remaining in thepot still after the first distillation of spirit is known as pot ale orburnt ale. The low wines are distilled for a second and sometimes athird time in spirit stills to produce raw spirit, which is matured inoak casks to produce malt whisky. The remaining liquor in the second andsubsequent distillations is called spent lees.

The by-products of the manufacture of malt whisky therefore comprisedraff, pot ale and spent lees. Draff contains the non-starch componentsof the original barley and generally represents about twenty fivepercent of the total malted barley added to the mash-tun. It is rich indigestible fibre and also contains concentrated protein and oil from themalted barley. It is palatable to all types of ruminant stock. Pot alehas low total solids content and contains dead yeast cells, yeastresidue, soluble protein, soluble nutrients, carbohydrates and othermaterial from the fermentation and mashing steps. It can also contain asignificant amount of copper from the stills themselves. Pot ale is richin nutrients and may be used as a feed for most ruminant stock. However,due to its high copper content, it is not suitable for sheep. Draff andpot ale are currently categorised as being of low economic value.

SUMMARY OF THE INVENTION

The inventors of the present application have developed a process forthe manufacture of butanol, acetone and/or other renewable chemicalswhich utilises low economic value by-products of the manufacture of maltwhisky, such as draff, pot ale and/or spent lees.

According to a first aspect of the present invention there is provided aprocess for the manufacture of butanol and/or acetone, comprising atleast the steps of:

-   -   treating a substrate comprising draff, or a derivative thereof,        and pot ale to hydrolyse the substrate to provide a treated        substrate, said draff comprising spent grain consisting        essentially of malted barley; and    -   fermenting the treated substrate in the presence of a culture of        butanol- and/or acetone-forming micro-organisms at an initial pH        in the range of 5.0 to 6.0 and at a concentration of free copper        ions of less than 20 μM to provide a fermented product        containing butanol and/or acetone.

In further aspects, the invention extends to the use of diluents otherthan pot ale, such as water, spent lees and spent liquid from otherfermentations.

Accordingly, according to a second aspect of the present invention thereis provided a process for the manufacture of butanol and/or acetone,comprising at least the steps of:

-   -   treating a substrate comprising draff, or a derivative thereof,        and a diluent to hydrolyse the substrate to provide a treated        substrate, said draff comprising spent grain consisting        essentially of malted barley; and    -   fermenting the treated substrate in the presence of a culture of        butanol- and/or acetone-forming micro-organisms at an initial pH        in the range of 5.0 to 6.0 to provide a fermented product        containing butanol and/or acetone.

In certain embodiments, the diluent is selected from the groupconsisting of pot ale, water, spent lees and spent liquid from otherfermentations, or a combination thereof. In particular, the diluent maybe water.

In further aspects, the invention extends to the use of biomasssubstrates other than draff. Examples of biomass substrates include, butare not limited to, municipal waste, industrial biological waste,agricultural crops and crop residues, wood and forestry waste, marinebiomass and bio-energy crops. Specific examples include paper, sludgefrom paper manufacture, spent grains such as those derived fromdistillers and brewers, fruit and vegetable waste, waste from the bakingindustry, seaweed and seaweed extracts, wood chip and other forestryderivatives, food crops, such as grain and crop residues, chocolate,algae (macro and micro algae), non-edible crops (and residues) andenergy crops, such as switchgrass.

Accordingly, according to a third aspect of the present invention thereis provided a process for the manufacture of butanol and/or acetone,comprising at least the steps of:

-   -   treating a biomass substrate, or a derivative thereof, and a        diluent to hydrolyse the substrate to provide a treated        substrate; and    -   fermenting the treated substrate in the presence of a culture of        butanol- and/or acetone-forming micro-organisms at an initial pH        in the range of 5.0 to 6.0 to provide a fermented product        containing butanol and/or acetone.

In certain embodiments, the substrate is paper, such as waste paper.

The diluent may be selected from the group consisting of pot ale, water,spent lees and spent liquid from other fermentations, or a combinationthereof. In particular, the diluent may be pot ale.

Accordingly, according to a fourth aspect of the present invention thereis provided a process for the manufacture of butanol and/or acetone,comprising at least the steps of:

-   -   treating a biomass substrate, or a derivative thereof, and pot        ale to hydrolyse the substrate to provide a treated substrate;        and    -   fermenting the treated substrate in the presence of a culture of        butanol- and/or acetone-forming micro-organisms at an initial pH        in the range of 5.0 to 6.0 and at a concentration of free copper        ions of less than 20 μM to provide a fermented product        containing butanol and/or acetone.

In certain embodiments, the substrate is paper, such as waste paper.

According to a further aspect of the present invention there is provideda biofuel comprising butanol and/or acetone manufactured according tothe process of any of the aspects of the present invention.

According to a yet further aspect of the present invention there isprovided use of one or more by-products of the production of malt whiskyin the manufacture of butanol and/or acetone by fermentation. In certainembodiments, the one or more by-products of the manufacture of maltwhisky comprise draff, pot ale and/or spent lees.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention utilise draff, pot ale,spent lees and/or other biomass substrates, such as waste paper. Inparticular, the present inventors have surprisingly discovered that itis possible to carry out fermentation in the presence of pot ale. It wasexpected that the high copper content in the pot ale from the copper potstills would inhibit butanol- and/or acetone-forming micro-organisms,such as bacteria of the genus Clostridium. However, the presentinventors have shown that when the substrate is diluted to lower theconcentration of free copper ions to below 20 μM, there is no inhibitoryeffect.

The use of pot ale in the manufacture of butanol, acetone and/or otherrenewable chemicals has several associated advantages. Pot ale iscurrently categorised as being of low economic value. The use of pot alein the present invention allows the economic value of pot ale to beincreased. Furthermore, the pot ale acts as a solvent to dissolve thesubstrate. Thus, the amount of water or other diluent required isreduced when pot ale is used. In addition, pot ale provides essentialnutrients to the microorganisms improving the fermentation and overallconversion of substrate to products.

The use of draff, spent lees and/or other biomass substrates in themanufacture of butanol, acetone and/or other renewal renewable chemicalsis also advantageous as it provides a solution to the disposal of thesesubstances. Draff, in particular, is currently categorised as being oflow economic value.

In certain embodiments, the draff, pot ale and/or spent lees areby-products of the manufacture of malt whisky. The use of theseby-products in the present invention thus allows low economic valueby-products to be recycled and offers a unique solution to the disposalof these by-products of malt whisky production.

In certain aspects, the present invention utilises biomass substrates,such as paper, and in particular waste paper. The present inventiontherefore further provides a solution to the disposal of waste paper,for example, old newspapers or used photocopier paper.

The substrate must be treated to hydrolyse it, thus breaking down thesubstrate into a form suitable for fermentation. Accordingly, in certainembodiments the substrate is subjected to one or more treatment steps tohydrolyse it, for example, mashing, heating, addition of acid or alkali,addition of enzymes or a combination thereof. In certain embodiments,the treating of the substrate to hydrolyse it comprises the step ofhydrolysing the substrate in the presence of water and hydrogen ions orwater and hydroxide ions. In certain embodiments, the treating of thesubstrate to hydrolyse it is carried out in the presence of any suitableacid which is capable of hydrolysing the substrate. Examples of suitableacids include sulphuric acid and nitric acid. Sulphuric acid is apreferred example of an acid for use in the present invention. Incertain embodiments, the treating of the substrate to hydrolyse itcomprises addition of one or more enzymes, such as cellulase andhemicellulase. In certain embodiments, a combination of treatments maybe utilised, for example, addition of both acid and enzymes, to providea treated substrate in a form suitable for fermentation. The combinationof treatments may be applied simultaneously or sequentially.

In certain embodiments wherein the substrate is draff and the diluent iswater, the treatment may comprise addition of enzymes. In alternativeembodiments wherein the substrate is draff and the diluent is pot ale,the treatment may comprise addition of acid and enzymes.

Fermentation of the treated substrate is carried out at an initial pH inthe range of 5.0 to 6.0, preferably in the range of 5.3 to 5.7 and morepreferably at 5.5. The use of this pH range has been shown to providehigh yields of butanol and/or acetone. Furthermore, this pH range allowsfermentation to be carried out without the need to remove solidstherefrom, thus reducing costs and avoiding any technical problemscaused by the requirement to remove solids. This pH range prevents anypotential toxicity from the treated substrate while maximising butanoland/or acetone production.

Fermentation is carried out in the presence of a culture of butanol-and/or acetone-forming micro-organisms. The butanol- and/oracetone-forming micro-organisms may be selected from any solventproducing micro-organisms which are capable of fermenting the substrateto form butanol and/or acetone. Suitable micro-organisms includemicro-organisms engineered to produce solvents. Examples of suitablemicro-organisms include those currently used in ABE(Acetone/Butanol/Ethanol) manufacture, and, in particular, bacteria ofthe genus clostridium such as C. acetobutylicum, C. beijerinckii, C.saccharoperbutylacetonicum and C. saccharobutylicum. In particularembodiments, the butanol- and/or acetone forming micro-organismscomprise C. acetobutylicum.

Fermentation is carried out at a concentration of free copper ions ofless than 20 μM. This ensures that the presence of the copper ions haveno/minimal negative effect. In certain embodiments, water or anotheraqueous solution may be added to lower the concentration of free copperions to below 20 μM free copper ions. In certain embodiments, theconcentration of free copper ions is less than 19, 18, 17, 16, 15, 14,13, 12, 11, 10, 9, 8, 7, 6 or 5 μM free copper ions during at least thefermentation step. In certain embodiments, the concentration of freecopper ions is less than 15 μM. In certain embodiments, theconcentration of free copper ions is less than 10 μM.

In certain embodiments, the treating and fermenting steps are carriedout simultaneously. This reduces the amount of time required, the numberof steps involved and the associated cost of manufacture.

In alternative embodiments, the treating and fermenting steps arecarried out sequentially. For example, draff may be pre-treated in twosteps, first with acid and then enzyme, prior to fermentation.

In certain embodiments, the fermented product further comprises one ormore of the compounds selected from the group comprising ethanol, carbondioxide, hydrogen, acetate and butyrate. Butanol and/or acetone may beseparated out of the fermented product using conventional separationtechniques. Alternatively, the fermented product may be used as a fuelor otherwise without further purification.

In certain embodiments wherein draff is utilised, the spent grainconsists of 100% malted barley.

In certain embodiments wherein the substrate comprises a by-product ofthe manufacture of malt whisky, the malt whisky is a Scotch malt whisky.

The term “biobutanol” as used herein refers to butanol made frombiomass.

The term “draff” as used herein refers to the composition of spentbarley solids and spent grain which remains in a mash-tun after theliquor (wort) has been drawn off in the manufacture of malt whisky.

The term “pot ale” as used herein refers to the liquor remaining in thewash (copper pot) still after the first distillation in the manufactureof malt whisky. It is the residue of the wash after extraction bydistillation of the low wines.

The term “spent lees” as used herein refers to the liquor remaining inthe distillation vessel after second and subsequent distillations in themanufacture of malt whisky. It is the residue of the low wines afterextraction by distillation of raw spirit.

The term “consisting essentially of malted barley” is understood hereinto refer to substrates which contain no, or only very minimal, types ofgrain other than malted barley. It therefore encompasses by-products ofthe manufacture of malt whisky. It is intended to encompass maltedbarley grains containing minor impurities other than other types ofgrain.

The term “concentration of free copper ions” refers to the concentrationof copper ions which is not bound to solids, that is, the concentrationof copper ions in the supernatant. The total concentration of copper inthe pot ale will be higher than the concentration of free copper ions assome copper remains bound to solids, such as dead yeast cells.

The term “Scotch whisky” as used herein refers to whisky made inScotland. In alternative embodiments, the malt whisky is a malt whiskymanufactured in other countries, such as Ireland or India, where theprocess for manufacture of malt whisky in that country is similar oridentical to the process used in Scotland for the manufacture of Scotchmalt whisky.

The present invention will now be described with reference to thefollowing examples which are provided for the purpose of illustrationand are not intended to be construed as being limiting on the presentinvention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the influence of initial pH on fermentation of acid andenzyme pre-treated draff in pot ale by C. acetobutylicum ATCC 824. Draffwas pre-treated with 0.08 M H₂SO₄ and the pH adjusted to between pH5.0-6.0 prior to enzyme addition. After enzyme hydrolysis, the pH wasadjusted to 4.5, 4.8, 5.0, 5.5, 6.0 or 6.5 for fermentation. FIG. 1 (a)shows sugars resulting from acid and enzyme treatment, FIG. 1 (b) showsresidual sugars after fermentation, FIG. 1 (c) shows the ABE productsfrom fermentation and FIG. 1 (d) shows yield of butanol and ABE fromdraff;

FIG. 2 compares ABE production by C. acetobutylicum ATCC 824 fromacid-pre-treated draff in either water or pot ale. After acid treatment,the pH was adjusted to pH 5.5 and enzymes and microorganisms added;

FIG. 3 shows ABE production by C. acetobutylicum ATCC 824 and C.beijerinckii NCIMB 8052 from draff at 1 L scale; and

FIG. 4 shows ABE production by C. saccharoperbutylacetonicum NCIMB 12606from (a) white office paper and (b) newspaper dissolved in either wateror 50% pot ale.

EXAMPLES

General Methods

The following organisms were used: C. acetobutylicum ATCC 824, C.beijerinckii NCIMB 8052 and C. saccharoperbutylacetonicum NCIMB 12606.Clostridia were maintained as spore suspensions at 4° C. Spores wereheat shocked at 80° C. for 10 minutes and inoculated into reinforcedclostridia media (RCM, Oxoid Ltd, Cambridge, UK). Cultures wereincubated for 24 hours and then subcultured into tryptone-yeastextract-ammonium acetate media (TYA) media containing glucose beforebeing used as a starting culture (at 5% v/v) for all experiments. TYAconsisted of (g/l) tryptone, 6; yeast extract, 2; ammonium acetate, 3;KH₂PO₄, 0.5; MgSO₄.7H₂O, 0.3; FeSO₄.7H₂O, 0.01 supplemented with 5%glucose. All clostridia cultures were incubated in an anaerobicworkstation under an N₂—H₂—CO₂ (80:10:10) atmosphere at 33° C. For 1 Lscale, fermentations were conducted in fermenters (Biostat A Plus,Sartorius Stedim Ltd, Surrey, UK). Oxygen-free conditions were achievedby sparging the media in the fermenters with oxygen-free N₂ for 1 hourprior to inoculation with clostridia. For all 1 L fermentations,agitation was set at 200 rpm and temperature at 33° C.

Wet draff, as received from the distilleries, had a moisture contentbetween 75-80%. Where stated, draff was dried at 80° C. to a moisturecontent of approximately 4% and milled prior to further processing.

Solvents (ethanol, acetone and butanol) were analysed using a Chrompack9001 gas chromatograph equipped with a flame ionisation detector and aCP SIL 5CB column of length 10 m and diameter 0.32 mm (all Chrompack,Middelburg, Netherlands). All samples were filtered through 0.2 μmcellulose acetate syringe filters before analysis and concentrationswere determined by reference to ethanol, acetone and butanol standards.

For acid (acetic and butyric) and monosaccharide (glucose, xylose andarabinose) analysis, samples were filtered through 0.2 μm syringefilters and acidified with H₂SO₄. Samples were analysed by HPLC using aVarian 920 LC fitted with integrated UV-VIS dual wavelength andrefractive index detectors (Varian Ltd., Oxford, UK). Components wereseparated at room temperature on a Rezex ROA Organic acid H⁺ 8% 300×7.8mm column (Phenomenex, Cheshire, UK) with 0.005 N H₂SO₄ as the mobilephase at a flowrate of 0.5 ml/min. Acids were detected at 210 nm whilesugars were detected with the RI detector and concentrations weredetermined by reference to the corresponding standards.

Example 1—Composition of Draff

Draff was collected from three different malt distilleries in Scotland.The monosaccharide composition of the draff was analysed according tothe Laboratory Analytical Procedure developed by the National RenewableEnergy Lab for the analysis of structural carbohydrates (Sluiter et al.,2008. NREL. Laboratory analytical procedure for the determination ofstructural carbohydrates and lignin in biomass. NREL/TP-510-42618). Theresults of the analysis are provided in Table 1. Glucose, xylose andarabinose were the predominant sugars, with very low levels of galactose(less than 2%) and no mannose detected. There was little variation inthe sugar composition of draff from different distilleries. Based onthese values, complete hydrolysis of draff (10.5% dry draff (w/v) asused in the experiments detailed below) should yield approximately 50g/I monosaccharide.

TABLE 1 Monosaccharide composition of draff Sugar (g/100 g draft) SourceGlucose Xylose Arabinose Total Distillery 1 20.9 ± 0.2 21.3 ± 0.1 9.0 ±0.2 51.2 ± 0.2 Distillery 2 18.4 ± 0.2 21.3 ± 0.2 9.2 ± 0.0 48.8 ± 0.4Distillery 3 20.5 ± 0.0 21.6 ± 0.3 9.3 ± 0.0 51.3 ± 0.3

Example 2—Effect of pH Control on Solvent Production by Clostridia

The effect of pH on fermentation of glucose in TYA media by C.acetobutylicum ATCC 824 was investigated. Fermentations were conductedat 1 L scale and the pH was controlled at a range of set points betweenpH 4.5-6.5 with automated addition of either alkali or acid. At pH 4.5,no glucose utilisation, acid or ABE production was detected. For allother fermentations, glucose was completely consumed within 48 hours andacids (butyric and acetic) and solvent (acetone, butanol and ethanol)were produced (Table 2). ABE production was highest at pH 4.8 and 5.0,corresponding to yields of 0.34 and 0.30 g ABE/g sugar, respectively.Acid production increased between pH 5.5 to 6.5, with a correspondingdecrease in conversion of sugar to ABE. At pH 6.5, acids only wereproduced with final concentrations of 7.8 and 12.8 g/I acetic andbutyric acid, respectively.

TABLE 2 Conversion of 5% glucose to acid and ABE by C. acetobutylicumATCC 824 in TYA media controlled at either pH 4.8, 5.0, 5.5, 6.0 or 6.5.Acid (butyric and acetic) and ABE concentrations were determined after68 hours with ABE yield expressed as g of ABE produced per g of sugarconsumed. pH Acid (g/l) ABE (g/l) Yield (g ABE/g sugar) 4.8 0.7 15.20.34 5.0 0.9 14.3 0.30 5.5 7.9 12.3 0.25 6.0 13.6 6.7 0.13 6.5 20.5 0.60.01

Example 3—Pot Ale as a Growth Medium

Pot ale was collected from a Scottish malt distillery and analysed forcopper content. The pot ale had 71.8 μM total Cu of which 21.1 μM wasdetermined to be available as “free” Cu in the supernatant with the restbound to the solids. To assess whether this Cu concentration was toxicto C. acetobutylicum ATCC 824, fermentation of 5% glucose in 100 ml TYAmedia supplemented with different concentrations of Cu was compared(Table 3). Cu had no effect on ABE production at 5 and 10 μM with ABEconcentrations of approximately 12 g/I being similar to that of thecontrol without Cu. At the higher Cu concentration, ABE concentrationwas reduced to 8.6 g/l, indicating that at this concentration Cu wasinhibitory to clostridia. As the pot ale had a “free” Cu content of 21.1μM, it was decided to test clostridia fermentation in half strength potale in order to reduce the Cu concentration below inhibitory levels.Half-strength pot ale supplemented with glucose provided enoughnutrients for growth of 824 with ABE production similar to the TYAcontrol (Table 3).

TABLE 3 Conversion of 5% glucose to ABE by C. acelabutylicum ATCC 824 ineither TYA, TYA containing 5, 10 or 20 μM Cu or 50% pot ale. Media ABE(g/l) TYA 12.4 ± 0.3 TYA, 5 μM Cu 12.3 ± 0.3 TYA, 10 μM Cu 11.6 ± 0.1TYA 20 μM Cu  8.6 ± 2.0 50% pot ale 12.0 ± 1.7

Example 4—Influence of Initial pH on Fermentation of Hydrolysed Draff

The effect of initial pH on fermentation of pre-treated draff wasinvestigated. Dried, milled draff was pre-treated by adding 10.5% (w/v)to 250 ml duran bottles with 0.08 M H₂SO₄ in 50% pot ale and sterilisedat 121° C. for 15 min. After cooling, the pH was adjusted to between pH5.0-6.0 by addition of 10 M NaOH and incubated with cellulase andhemicellulase enzymes at 33° C. for 24 hours. For fermentation, the pHof the solutions was adjusted to either 4.5, 4.8, 5.0, 5.5, 6.0 or 6.5prior to inoculation with C. acetobutylicum ATCC 824. The initial sugarconcentration was monitored before fermentation and the residual sugar,ABE concentration and ABE yield were calculated after fermentation (FIG.1). The initial concentration of sugars was similar for all samples,with approximately 9.6, 11.2, and 9.9 g/l glucose, xylose and arabinose.No growth or gas production was apparent at pH 5.0 or lower and nosugars were utilised. ABE production was greatest at pH 5.5 (14.2 g/I)with a yield of 13.2 g/100 g draff. This was reduced at pH 6.0, with 9.3g ABE/100 g draff. At pH 6.5, approximately half the sugar was utilisedbut there was poor conversion to ABE with a final concentration of 2.3g/l.

Example 5—Fermentation of Acid Pre-Treated Draff in Pot Ale or Water

Dried, milled draff (10.5% w/v) was pre-treated with 0.08 M H₂SO₄ ineither water or pot ale in 250 ml duran bottles by sterilisation at 121°C. for 15 minutes. After cooling the pH was adjusted to 5.5 by theaddition of 10 M NaOH. Cellulase and hemicellulase enzymes and C.acetobutylicum ATCC 824 inoculum were added and bottles incubated at 33°C. The ABE concentration was determined after fermentation (FIG. 2). Fordraff in water, ABE yield was 14.0 g ABE/100 g draff whereas in pot ale,a yield of 14.9 g ABE/100 g draff resulted.

Example 6—Conversion of Draff to Butanol and Acetone at 1 L Scale

Draff (10.5% w/v) was pre-treated with 0.08 M H₂SO₄ in 50% pot ale in 1L fermenters by sterilisation at 121° C. for 15 minutes. In this casedraff was used wet, as received from the distillery, without any furtherprocessing. After cooling to 33° C., the pH was adjusted to pH 5.5 bythe addition of 10 M NaOH and the fermenters were sparged with N₂. Afterdegassing, enzymes and either 824 or 8052 were added and solvents wereanalysed at the end of the fermentation. Fermentation by C.acetobutylicum ATCC 824 and C. beijerinckii NCIMB 8052 resulted in ABElevels of 11.3 and 12.8 g/l, respectively (FIG. 3). This corresponded toconversion rates of 10.6 and 12.1 g ABE per 100 g draff, respectively.

Example 7—Process for Conversion of Waste Paper to Butanol and Acetone

White office paper and newspaper were shredded to 5 mm wide strips and6.7% (w/v) was mixed with either water or 50% pot ale in 250 ml duranbottles and the pH adjusted to pH 5.5. After sterilisation, the bottleswere cooled and cellulase and C. saccharoperbutylacetonicum NCIMB 12606added. After fermentation, the ABE concentrations were determined (FIG.4). There was poor conversion of paper to ABE in water compared to potale, demonstrating that pot ale was required to provide additionalnutrients. In pot ale, the ABE yields after fermentation with C.saccharoperbutylacetonicum were 24.8 g ABE per 100 g office paper and16.8 g ABE per 100 g newspaper.

Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiments.Indeed, various modifications of the described modes of carrying out theinvention which are obvious to those skilled in the art are intended tobe covered by the present invention.

1. A process for the manufacture of butanol and/or acetone, comprising at least the steps of: treating a substrate comprising draff, or a derivative thereof, and pot ale to hydrolyse the substrate to provide a treated substrate, said draff comprising spent grain consisting essentially of malted barley; and fermenting the treated substrate in the presence of a culture of butanol- and/or acetone-forming micro-organisms at an initial pH in the range of 5.0 to 6.0 and at a concentration of free copper ions of less than 20 μM to provide a fermented product containing butanol and/or acetone. 